Firstly you should look at the common themes between both texts, as well as the similarities between Donne and Vivian eg. they both experience an existential crisis, they both use wit/intellect to deal with the confronting nature of death, etc
However, since it is a comparative, you should also include the impact of the texts' contexts on those similarities eg. in Donne's context, natural life processes were believed to be controlled by God, whilst in Edson's context, science is believed to be the 'higher power', since Vivian's life is essentially in the hands of modern medicine
So with your notes you could maybe create tables that compare both Donne and W;t?? But I also definitely recommend reading stuff online about these two texts because that definitely helped me a lot. Hope you find this helpful!